1. Field of the Invention
The present invention relates to a focus state display device for use in a camera which is adapted to effect focusing to an object in one of plural focus detection areas within the phototaking image field of said camera.
2. Related Background Art
In the field of conventional cameras, there are already known devices for displaying an area in which the focus detection is to be conducted or a focus state.
FIGS. 1 and 2 are respectively a cross-sectional view and a plan view of a conventional focus state display device, for use in a camera, disclosed in the Japanese Patent Laid-open Application No. 56-99332.
In these drawings there are shown a photo-taking lens 1; a quick-return mirror 2 and a focusing screen 3 provided, for example, with a Fresnel lens thereon. The light entering the phototaking lens 1 is reflected by the mirror 2 and focused on the focusing screen 3.
A focus state display plate 4, composed of a flat transparent substrate, is provided at the central part thereof with a display area 5 consisting of a group of microprisms, as shown in FIG. 2. An illuminating LED 6 is positioned at the side of the display plate 4, and directed toward the display area 5. The light from said illuminating LED 6 enters the display plate 4 through a light-guiding prism 7, then is repeatedly reflected by the upper and lower faces of said display plate 4 and reaches the display area 5, thus illuminating the same.
There are further provided a condenser lens 8, a pentagonal prism 9, and an eyepiece lens 10, through which the image focused on the focusing screen 3 can be observed.
When the illuminating LED 6 is not turned on, the display area 5 appears as a shadow, thus indicating the focus detection area. The LED 6 is turned on when the in-focus state is reached in the course of focus detecting operation, whereby the display area 5 is illuminated in superposition with the image shown in the view finder and can therefore be utilized for the display of focus state. The photographer observes simultaneously the object image in the view finder and the shadow of the display area 5 indicating the focus detection area, and manually focuses the phototaking lens so as that said display area 5 is turned on.
FIG. 3 is a plan view showing another conventional example of the focus state display device, for use in a camera, as disclosed in the Japanese Patent Laid-open Application No. 56-99332. In this example, a display area 5 is divided into partial display areas 5a, 5b arranged in lateral direction and respectively formed in the form of arrows, and a pair of illuminating LED's 6a, 6b are provided respectively corresponding to said partial display areas 5a, 5b. The partial display area 5a at the left is turned on in the so-called rear focused state, while that 5b at the right is turned on in the front focused state, and both areas 5a, 5b are turned on when the photo-taking lens is adjusted to the in-focus state. Consequently the photographer can effect the focusing of the phototaking lens, while continuously watching the image in the view finder.
FIG. 4 is a plan view showing a conventional example of a focus detection area display device, for use in a camera, disclosed in the Japanese Patent Laid-open Application No. 1-288845.
The camera of this conventional example is capable of focus detection in plural areas in the image field. Consequently the display plate 4 is provided with plural display areas 5, and illuminating LED's 6 are provided in a corresponding number. In case of such multi-area focus detection, it is necessary to indicate the area in which the focus detection is to be conducted, and, for this reason, upon selection of a focus detection area, a corresponding display area 5 is turned on.
However, in a camera having plural focus detection areas as shown in FIG. 4, if the display area 5 is turned on for the purpose of indicating the selected focus detection area, said lighted display area 5 can no longer be used for indicating the in-focus or out-of-focus state in the manner as shown in FIGS. 1 and 2.
On the other hand, if the in-focus or out-of-focus state is indicated by the lighting of the display area 5, it is not possible to indicate the focus detection area since no area is lighted in the out-of-focus state. In a camera with plural focus detection areas, if the display of the focus detection area is not available, the photographer is unable to obtain information on said area from the image in the view finder during the focusing operation of the phototaking lens. Consequently the photographer may become uncertain about or forget the selected focus detection area, in case the focusing operation takes a long time for the confirmation of focus state of the background scene or in case the observation of the view finder is interrupted for reconfirming the object.
Such drawbacks can be prevented by dividing, as shown in FIG. 3, each display area 5 into small display areas 5a, 5b and lighting either for indicating the focus detection area. However, such structure will require plural small display areas 5a, 5b and corresponding LED's 6 for each of the plural display areas, thus leading to an increased number of light emitting devices and optical components and eventually to an increased cost and an increased dimension of the camera. Also the distance between the small display areas 5a, 5b along the lateral direction of the display plate 4 becomes smaller than in the conventional device, so that the illumination of a small display area may induce illumination of the neighboring small display areas by stray light.